Porous article impregnation



ilnited States Patent POROUS ARTICLE IMPREGNATION Hooper J. Houck, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application August 8, 1952, Serial No. 303,417

4 Claims. (Cl. 204-37) This invention relates to a method for impregnating porous metal parts with a lower melting point metal.

It is therefore an object of the invention to provide a method for impregnating porous metal parts with a lower melting point metal wherein dissolving action of the lower melting point metal on the part to be impregnated is substantially eliminated. v

A further object of the invention is to provide a method for impregnating porous ferrous parts with cupreous metal wherein the dissolving action of copper on iron is substantially eliminated.

A still further object of the invention is to provide a method for impregnating the porous metal parts with another metal of lower melting point wherein said other metal is predeterminately arranged with respect to said part prior to the actual impregnating step.

in carrying out the above object, it is a further object to provide the impregnating metal in a uniform state of distribution with respect to the part to be impregnated as by plating or spraying.

Further objects and advantages of the present invention will be apparent from the following description.

in the impregnation of porous metal parts, numerous expedients havebeen proposed to prevent erosion and channeling of the porous part when the impregnation is carried out with a metal that has a dissolving action on the part. The impregnation of ferrous parts with cupreous metals falls within this class since copper has a marked dissolving action upon iron at the temperature of impregnation, namely, at a temperature above the melting point of copper or copper alloy. This dissolving effect causes a channeling or pitting at the surface of the iron part at the point of entry of the copper.

I have found that this dissolving action can be greatly reduced by proper distribution of the impregnating metal so that the point of entry of said metal is uniformly spread over a large area rather than through one small sector thereof whereby the copper-iron ratio is maintained at a minimum.

Distribution of impregnating metal is a diflicult problem, however, since where an entire part is to be impregnated, proper distribution requires a complete covering of the part by a uniform layer of the impregnating metal. Similarly, where only a section of a part is to be impregnated, the impregnating metal should be uniformly distributed over that section.

I have found that the advantageous distribution of the impregnating metal with respect to the metal to be impregnated can be accomplished by plating. That is to say the part to be impregnated, such as the porous iron part, may be placed in a plating tank and the cupreous metal plated thereover in a uniform layer wherein the plate even enters portions of the porous structure of the part. The extent of plating is determined by the extent of impregnation desired and in this connection, the plate may be deposited very rapidly with little or no concern for the quality of the plate since the only point of the plating procedure is 2,756,200 Patented July 24, 1956 to obtain a uniform distribution of the impregnating metal on the part.

After the part has been plated, it is washed and dried and is then heated to a temperature above the melting point of the plate whereupon the plate melts and is drawn by capillarity into the porous structure of the article.

It will be apparent that if copper is used on porous iron, the distribution of copper is very uniform in the electroplate and therefore at no one portion of the porous iron part does any great amount of copper have to enter, which uniform distribution, therefore, reduces tremendously the tendency toward dissolving.

I have found in many instances, instead of electroplating, the impregnating metal may be disposed upon the surface of the porous metal part by spraying such as from a Shoop gun. In this manner, any suitable metal may be sprayed upon the surface of the porous metal part in any desired and predetermined thickness. If the part is to be completely covered, it may be placed in a fixture or barrel which causes rotation and or movement before the gun so that a uniform layer is deposited thereon. If only a portion of the part is to be impregnated, the part may be masked or that portion of the part only may be placed within the aim of the gun so that that portion only receives the deposition.

Still another means of depositing the impregnating metal in a uniform manner on the part to be impregnated and in predetermined relation thereto is by utilizing metal powder in lacquer, for example, whereby copper powder mixed with a suitable heat-destructible lacquer, such as cellulose, may be sprayed onto the surface of the part in any predetermined manner so as to produce a uniform layer over the entire part or at selected portions thereof.

If complete impregnation is desired, it may be useful to include some of the techniques as discussed in the Bourne Patent No. 2,401,221 or copending application to i A. L. Boyce, Serial No. 289,271, assigned to the assignee of this invention, wherein additions of iron, for example, are made to the copper impregnant to satisfy its dissolving action to some extent upon the part to be impregnated. That addition may be coplated with copper onto the surface of the iron or may be codeposited from a Shoop gun or from a lacquer gun. This expedient has been found to be unnecessary in most cases, although it may be useful Where a selected area of a part is to be fully impregnated in which case a large quantity of the impregnant must enter the part through a restricted area thereof.

Selective impregnation may be suitably carried out under the teachings of copending application of A. L. Boyce, Serial No. 303,441, assigned to the assignee of this invention, wherein localized heating of the part is used for obtaining a sharp line of demarcation between impregnated and unimpregnated portions of the part. Any of these expedients come within the scope of this invention which is broadly directed to the plating, either by electrodeposition, metallizing methods or paint spray applications, etc., of a porous metal part with the impregnating metal, wherein the impregnating metal is disposed in a uniform layer at any selected portion thereof or over the entire part.

A specific example of such a procedure contemplates the impregnation of a porous ferrous part with a cupreous metal, such as copper. The copper is plated in desired thickness upon the part which is then washed with water and dried, is then passed through a furnace maintained at a temperature above the melting point of copper and well below the melting point of iron, for example, at about 2050 F., whereupon the electroplate melts and is drawn by capillarity in the pores of the porous ferrous part. Another example contemplates the impregnation of a porous bronze article with lead wherein the lead is electroplated, sprayed or otherwise applied in a uniform layer and in a given quantity over all the porous surface of the bronze part which is then heated to a temperature below 1400" F. and above the melting point of lead for causing the lead to melt and to be drawn into the pores of the bronze part for impregnating the same.

If a selective impregnation of a given portionof an article is to be carried out, the given portion of the article may be masked from the remainder of the article and impregnating metal may be sprayed onto said selected portion in a desired thickness of coating either by a Shoop gun or a paint spray gun whereby the part is preferably placed in an induction apparatus which will selectively heat any portion of the article to be impregnated to a temperature above the melting point of the impregnating metal and below the melting point of the metal to be impregnated whereupon the impregnating metal melts and is drawn by capillarity into the selective heated portion of the article. i

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a method for impregnating a porous ferrous article with a cupreous metal wherein a uniform impregnation is accomplished without pitting or channeling of the porous ferrous article, the steps comprising; plating the surface only of a porous ferrous article with a uniform covering of a cupreous metal wherein the plate thickness is sufiicient to ultimately provide the desired impregnation, heating the plated article at a temperature above the melting point of copper and below the melting point of iron for a time suflicient to melt the cnpreous plate, and then uniformly References Cited in the file of this patent UNITED STATES PATENTS 880,405 Schmidt Feb. 25, 1908 2,195,499 Schofield Apr. 2, 1940 2,363,337 Kelly Nov. 21, 1944 2,390,805 Merryman Dec. 11, 1945 2,401,221 Bourne May 28, 1946 2,561,579 Lenel July 24, 1951 2,581,252 Goetzel Jan. 1, 1952 2,612,443 Goetzel Sept. 30, 1952 

1. IN A METHOD FOR IMPREGNATING A POROUS FERROUS ARTICLE WITH A CUPREOUS METAL WHEREIN A UNIFORM IMPREGNATION IS ACCOMPLISHED WITHOUT PITTING OR CHANNELING OF THE POROUS FERROUS ARTICLE, THE STEPS COMPRISING: PLATING THE SURFACE ONLY OF A POROUS FERROUS ARTICLE WITH A UNIFORM COVERING OF A CUPREOUS METAL WHEREIN THE PLATE THICKNESS IS SUFFICIENT TO ULTIMATELY PROVIDE THE DESIRED IMPREGNATION, HEATING THE PLATED ARTICLE AT A TEMPERATURE ABOVE THE MELTING POINT OF COPPER AND BELOW THE MELTING POINT OF IRON FOR A TIME SUFFICIENT TO MELT THE CUPREOUS PLATE, AND THEN UNIFORMLY DRAWING SAID MOLTEN CUPREOUS METAL INTO THE PORES OF SAID POROUS FERROUS ARTICLE BY CAPILLARITY, WHEREBY THE COPPERIRON RATIO THROUGHOUT THE ENTIRE SURFACE OF THE POROUS FERROUS ARTICLE IS MAINTAINED AT A MINIMUM. 